Designing a switch matrix module that can handle large current loads and that can also have a high frequency bandwidth in a small footprint is no easy task to accomplish. As the dimensional size of a switch matrix increases, signal path lengths typically increase, causing a degradation of the signals being transmitted through the switch matrix.
N×M switch matrices generally are classified into one of three types: cross-point, blocking, or non-blocking. An example 2×2 switch matrix constructed as a non-blocking switch matrix is shown in the FIG. 1, a 2×2 blocking matrix is shown in FIG. 2, and a 2×2 crosspoint matrix is shown in FIG. 3.
In order to better understand these different switch matrix types, a discussion of some of the advantages and disadvantages of each type of switch matrix follows.
Non-Blocking Switch Matrices
A prior art non-blocking switch matrix as shown in FIG. 1 provides the highest frequency capabilities of any of the other types of switch matrices, well into the Giga-Hertz (GHz) range with appropriate switch selection. An N×M non-blocking switch matrix allows up to the smaller of N or M simultaneous and independent paths while minimizing or eliminating stubs that generate high Voltage Standing Wave Ratios (VSWRs).
One disadvantage found with non-blocking switch matrices is that they are the least space efficient of all three matrix types since the size of the matrix determines the number of switches and poles required. Hence an 8×8 switch would require 16 separate 1×8 switches to implement. Non-blocking switch matrices make it difficult to route electrical interconnections on printed circuit boards. Such interconnections are typically implemented in practice using discrete coaxial cable connections which create a bulky, space-inefficient situation. Non-blocking switch matrices are also difficult to use as a building block for a larger sized switch matrix since even more difficult interconnects would be required.
Blocking Switch Matrices
Blocking switching matrices as shown in FIG. 2 have the highest operating frequency potential, well into the GHz range with appropriate switch selection. These switch matrices also use up a very small footprint and require only one switch with N poles and another with M poles. Another advantage of the blocking switch matrices is that they require single cable interconnects which minimizes the tangling of cables.
Some of the disadvantage inherent with blocking switch matrices is that they are difficult to use as building blocks to build larger-sized switch matrices a major disadvantage in some applications. Also, blocking switch matrices only allow for a single electrical signal path to exist at any given point in time.
Cross-Point Matrices:
Cross-point matrices such as that shown in FIG. 3 have the highest density potential of all matrix types and as such are conducive to printed circuit board layout designs. An N×M cross-point matrix allows up to the smaller of N or M simultaneous and independent paths. A cross-point matrix also makes it easy to replace relays when a printed circuit board layout design is used for interconnects. Other advantages of cross-point matrices are that they have relatively few internal interconnects: N+M, provide for single cable interconnects and are easy to use as building blocks to create larger matrix sizes on the same circuit board.
A disadvantage of cross-point matrices is that stubbing is difficult to control on larger matrix sizes and can seriously deteriorate higher frequency performance if not controlled. Cross-point matrices also have frequency performance characteristics significantly less than the other matrix types, in the MHz range versus GHz for the other types since high-frequency (“can”) switches do not have a physical geometry conductive to this matrix layout. Cross-point switch matrices also make it difficult to build larger matrix sizes where the matrices span different circuit cards (modules) without creating additional stubbing problems.